1. Field of the Invention
The present invention relates to a fuel cell power generation apparatus, a fuel cartridge, and a fuel cell system using the same. In particular, the invention relates to a fuel cell system in which the amount of a reaction product discharged outside the system can be reduced, the reaction product, such as water, being formed by the electrochemical reaction of a fuel cell.
2. Description of the Related Art
A fuel cell is a device for generating electrical energy from hydrogen and oxygen and is capable of providing high power generation efficiency. One of the main features of a fuel cell is that high power generation efficiency can be expected even in small-scale systems since, in contrast to a conventional power generation method in which the power is generated via a thermal or kinetic energy process, the power is generated through direct power generation. Another feature is that environmental friendliness is excellent since the emission of nitrogen compounds and the like is low, and noise and vibrations are also small. As mentioned above, a fuel cell can effectively utilize the chemical energy contained in fuel and has environmentally friendly characteristics. Therefore, a fuel cell is expected to serve as an energy supply system of the 21st century and has received attention as a new promising power generation system usable in various applications including small to large scale power generation, for example, in space, automobile, and portable device applications. Thus, the technological development of a fuel cell for practical use is fully in progress.
Among various types of fuel cells, a proton-exchange membrane fuel cell can operate at lower temperatures and generate power at higher power densities as compared to other types of fuel cells. Particularly in recent years, a direct methanol fuel cell (DMFC) has received attention as a form of the proton-exchange membrane fuel cell. In the DMFC, methanol aqueous solution serving as a fuel is directly supplied to an anode without modification to obtain electric power through the electrochemical reaction of the methanol aqueous solution with oxygen. In this electrochemical reaction, carbon dioxide serving as a reaction product is discharged from the anode, and product water serving as a reaction product is discharged from a cathode. As compared to hydrogen, methanol aqueous solution has higher energy per unit volume and a lower risk of explosion or the like and is suitable for storage. Thus, the DMFC is expected to be employed as a power source for an automobile, a portable device, and the like.
In such fuel cells, water is formed by an electrochemical reaction (a reaction for power generation). A compact fuel cell (a so-called passive type fuel cell) utilizing spontaneous diffusion of fuel and air is expected to be employed in portable devices such as a cellular phone, a notebook type personal computer, a PDA, an MP3 player, a digital camera, and an electronic dictionary (book). Particularly, in the structure for such a compact fuel cell, the formed water is directly discharged to the outside as liquid or vapor together with discharge air, and the portable device itself or the outside thereof could get wet. In view of the above, in Japanese Patent Laid-Open Publication No. 2004-241363, a structure is employed in which the outer periphery of an air intake is covered with a water absorbent material to bring the water absorbent material into contact with a cathode where water is formed. In this manner, water is prevented from being discharged to the outside in a liquid state.